The Thompson Weinman process is widely employed to separate impurities from limestone rock. In such a process the mineral bearing rock is subjected to flotation. To effect separation of mineral impurities from calcite, the ground ore is subjected to flotation in the presence of xanthate or tallow amine and/or imidazoline reagents. A particular combination which has been used is a mixture of sodium sec-butyl xanthate and an alcohol type material in amounts of 0.25 to 0.5 pound per ton of calcite ore to float pyrite impurity from the ore. Although such a composition is useful to remove pyrite impurities, it has become common practice to add other flotation reagents such as a combination of N-tallow-trimethylenediamine diacetate and a tertiary amine having one fatty alkyl group and two polyoxyethylene groups attached to nitrogen. This removes, in addition to the pyrites, other insoluble impurities, such as micaceous schist and quartz. These combinations have been found to have certain disadvantages, however, among which are a tendency to promote the corrosion of iron and steel in the reaction vessels leading to brown tints in the calcite pigment and a tendency to act as dispersants for the finely divided calcite in the system, making longer settlement times necessary.
In Stanley et al., U.S. Pat. No. 3,990,966, is described a process in which impurities are separated from calcite by grinding calcite ore, separating the impurities from the calcite by conditioning the ground ore with a cationic flotation reagent selected from the group consisting of 1-hydroxyethyl-2-heptadecenyl glyoxalidine and 1-hydroxyethyl-2-alkylimidazolines and salt derivatives thereof, wherein the alkyl portion of the imidazoline is the alkyl portion of a fatty acid, dry or wet classifying the separated calcite and, if wet, settling the classified calcite in a thickener in the presence of an anionic settling agent. Such a process avoids many of the drawbacks of the prior art, primarily because the normally liquid flotation agents are easier to handle than the solid agents of the prior art and the flotation agents of Stanley et al are much less corrosive.
It has now been discovered that the use of alkoxylated alkyl guanidines and/or alkoxylated alkyl amines in the flotation of the deleterious minerals results in overall higher calcium carbonate recoveries compared to the collectors used in the present state of the art (for example, Stanley et al).
With the reagents of the present invention, flotation may be used to achieve acceptable calcium carbonate product brightness levels for use in filler applications where product brightness is important. Achievement of the calcium carbonate target brightness specification is dependent on the efficient removal, by the collectors (i.e.,flotation agents) of the present invention, of certain minerals, such as micas, feldspars, etc., from the calcium carbonate product. Additionally, removal of silica (quartz) is also desirable and the presently developed reagents remove silica very effectively so as to produce calcium carbonate with lower product abrasiveness and its concomitant deleterious effect on equipment where the final calcium carbonate product is used. Finally, flotation employing the reagents of the present invention affects in a very positive manner the calcium carbonate product's brightness, yellowness and whiteness values. This will be established after consideration of the experimental data hereinafter which compares the effect of the alkoxylated alkyl guanidines and/or alkoxylated alkyl amines on increasing brightness and lowering acid insolubles levels with those of state-of-the-art imidazolines.